1. Field of the Invention
The present invention relates generally to a method and apparatus for evacuating refrigerant from a storage device or an appliance or system containing refrigerant, and more particularly, to a method and apparatus including a self-clearing, vacuum pump with external, forced-air cooling that can operate with a positive inlet and/or outlet pressure and is adapted for obtaining a deep vacuum to completely evacuate refrigerant from an appliance, refrigerant system, or storage device.
2. Description of the Related Art
The Clean Air Act was enacted in 1990 and is enforced by the Environmental Protection Agency (EPA) which has passed a number of regulations to limit and regulate the use of refrigerants to limit the harmful effects of atmospheric ozone depletion by chlorine-based refrigerants. Significantly, the EPA regulations make it illegal to intentionally discharge or vent refrigerants into the atmosphere and require EPA certification of equipment used for recovery, reclaiming, and recycling of refrigerants (i.e., the three standard processes used to remove refrigerant from a system or storage device and to clean the removed refrigerant). This has resulted in a demand for equipment or machines for recovering, recycling, and reclaiming refrigerant that meet the EPA requirements. In general, recycling machines are used to remove a refrigerant from an appliance or storage container and to clean the refrigerant for reuse, typically by passing the refrigerant through an oil separator to remove contaminated oil and through devices that at least partially reduce moisture, acidity, and particulate matter. In contrast, reclaiming machines are more complex devices used to process refrigerant to the purity specified in American Refrigeration Institute standards, i.e., the reclaimed refrigerant typically needs to be clean or cleaner than new refrigerant. In general, recovery machines are devices used to remove refrigerant in any condition from an appliance or storage container and to transfer or pump the removed refrigerant to another container for storage without further processing.
In an attempt to control the discharge of refrigerant to the atmosphere, the EPA established minimum levels of evacuation to be met when recovery, recycling, and reclaiming machines are used to evacuate refrigerant from appliances and storage containers, i.e., a level of evacuation that leaves relatively small amounts of refrigerant in the appliance or container which can then be vented or discharged to the atmosphere. For example, the EPA has established the following evacuation levels for high-pressure appliances, as measured in inches of mercury (Hg) vacuum (relative to standard atmospheric pressure of 29.9 inches mercury (Hg)): (1) 0 inches for HCFC-22 appliances containing less than 200 pounds (liquid weight of refrigerant); (2) 10 inches for HCFC-22 appliances containing more than 200 pounds; (3) 10 inches for CFC-12, CFC-500, CFC-502, and CFC-114 appliances containing less than 200 pounds; and (4) 15 inches for CFC-12, CFC-500, CFC-502, and CFC-114 appliances containing more than 200 pounds. For the purposes of this patent, any vacuum level below about 3 to 4 inches Hg, and more particularly, below about 10 inches Hg, is considered a "deep vacuum." Unfortunately, while providing an easily measured standard for evacuation, the EPA evacuation levels, especially the deep vacuum levels, have proven difficult to obtain using existing equipment.
In practice, a technician who wants to remove refrigerant from an appliance or storage device, to complete maintenance, clean the refrigerant, or otherwise, will connect the appliance or storage device to a recovery, recycling, or reclaiming device that draws the refrigerant out with its compressor. These devices may also include a condenser to change the refrigerant discharged from the compressor to a liquid for ease of storage in a cylinder or tank and may also include a heat exchanger located upstream of the compressor to allow evacuation of liquid refrigerant without causing damage to the compressor. By far, the most commonly used compressors in these devices are hermetic, reciprocating piston compressors in which the motor is sealed in the same housing as the compressor and is positioned within an external shell on internally mounted springs. A gap is left between the external shell and the motor to allow the motor to be isolated from compressor vibrations. In these types of compressors, the bottom portion of the external shell acts as an oil sump, and as the oil circulates and lubricates the internal moving parts, it picks up some of the compressor heat caused by friction of the moving parts, work performed during compression, and electric motor inefficiencies and transfers this heat to the external shell. To prevent overheating problems in these "low-side dome" compressors, the refrigerant that is suctioned, preferably at an inlet pressure of about 5 p.s.i.g. or greater, into the compressor is drawn through the motor windings and around the motor in the gap between the motor and external shell before it is taken into the compressor cylinder(s) to remove some of the heat developed by the motor from the compressor.
Because heat removal is almost completely dependent on the mass flow of refrigerant over the motor, the spring-mounted, reciprocating compressor can be ineffective in many circumstances in achieving the minimum evacuation levels (specifically, 10 or more inches Hg) required by the EPA. These compressors typically overheat prior to reaching the required evacuation levels because of the significant reduction in refrigerant flow, and the compressor either automatically trips off or simply "bums out." For example, when a recovery, recycling, or reclaiming machine with this type of compressor is used to evacuate a storage tank (e.g., a typical refrigerant storage tank has an internal volume of about 130 cubic feet), a technician connects the machine to the storage tank and operates the machine's compressor (e.g., a fractional horsepower, reciprocating compressor) to draw the refrigerant out for storage and/or processing. Although the evacuation of the storage tank progresses quickly when the tank is relatively full, e.g., charged at higher pressures, the process slows dramatically as the pressure in the storage tank is lowered from about 15 p.s.i.g. to atmospheric pressure (0 inches Hg) and slows even more as a vacuum is developed in the storage tank. The compressor operates below the refrigerant inlet pressure needed for adequate cooling until the compressor overheats, typically when 0 to 4 inches Hg vacuum or even no vacuum has been obtained on the storage tank. In this regard, U.S. Pat. No. 4,998,416 of Van Steenburgh, Jr. provides a reclaiming machine that injects small amounts of liquid refrigerant onto the motor coils when minimal amounts of refrigerant are entering the compressor inlet. However, even with this improved compressor cooling system, the compressor components begin to heat up rapidly at suction inlet pressures of about 5 to 15 p.s.i.g., which can result in compressor failure prior to obtaining a deep vacuum on the device being evacuated.
Because existing equipment and compressors are ineffective in achieving the EPA set evacuation levels, many technicians in the industry will only utilize the compressor of the recovery, recycling, or reclaiming machine to remove as much refrigerant as possible, which generally achieves a vacuum of 0 to 4 inches Hg in the evacuated device. During this operation, the technician may attempt to avoid damaging the compressor by monitoring the temperature of the compressor and manually shutting the machine off when the compressor begins to overheat. The technician will then connect a standard refrigerant vacuum pump to the device being evacuated to remove more of the refrigerant by drawing a vacuum and discharging the removed refrigerant to the atmosphere. As can be appreciated by those in the art, the standard vacuum pump typically will only operate with an inlet pressure of 0 p.s.i.g. or vacuum and an outlet pressure equal to atmospheric pressure or less, and the vacuum pumps generally employed are able to draw a vacuum of about 29.9 inches Hg at sea level as it discharges refrigerant to the atmosphere. At this level of vacuum, the device is considered by the technician to be "empty."
The inventor recognizes that due to the limitations of existing refrigerant equipment a technician may have problems fully and easily complying with the EPA regulations under a number of operating conditions. These problems in complying with the regulations can result in a significant amount of refrigerant being discharged to the atmosphere in violation of the premises of the Clean Air Act. In the above storage tank example, the following approximate weights of various types of refrigerant would be pumped into the atmosphere (assuming the vacuum pump was connected when 0 p.s.i.g. was obtained in the storage tank): 42 pounds of R-12, 30 pounds of R-22, 35 pounds of R-500, and 38 pounds of R-502. This is a significant discharge of refrigerant when it is understood that this magnitude of discharge occurs throughout the refrigerant industry each time refrigerant is evacuated from a storage tank and similarly, smaller amounts of refrigerant are discharged each time an appliance or smaller storage device is evacuated. Consequently, there is a strong environmental and legal need for an apparatus and method for more effectively evacuating refrigerant storage devices, appliances, and systems to meet the EPA minimum evacuation levels. Additionally, such a system would provide significant economic benefits by more fully capturing refrigerant which continues to increase in price and by reducing equipment costs by eliminating the need for repairing and replacing compressors.
Additionally, the inventor recognizes that even when the EPA's minimum evacuation levels are obtained, the storage device, appliance, or system will still contain a residual amount of refrigerant, i.e., not be fully empty. Although the residual amount is not as large as the amount removed between 0 and 15 inches Hg vacuum, it is believed to be a large enough amount to make it economically desirable to capture the residual amount of refrigerant. This additional evacuation step also provides a more fully evacuated storage device, appliance, or system which may reduce possible discharges to the atmosphere and reduce maintenance problems that may arise from mixing of refrigerant and oils if a different refrigerant is charged into the storage device, appliance, or system. Consequently, it is desirable to provide an apparatus and method for providing additional evacuation of refrigerant devices to remove at least a portion of residual refrigerant remaining after EPA evacuation levels are achieved.